Radiation is known to cause cancer. On average, we receive about 0.3 rads/year of high energy radiation. Rad (radiation absorbed dose, 1 rad=10 mSv) is one of the units of radiation exposure. According to the US Nuclear Regulatory Commission (NRC) guidelines, the maximum permitted dose for an occupational radiation worker is 5 rads/year, not to exceed 25 rads for the life. There is no easily detectable clinical effect in humans up to 25 rads. However, on average, if 2,500 people are exposed to one rad of radiation, one is expected to die of radiation induced cancer. Hence, we need to minimize the exposure and should monitor radiation exposure from very low dose, e.g., 10 millirads to lethal dose, e.g., a few thousand rads.
A large number of radiation detectors, monitors, and dosimeters are used for detecting and monitoring radiation. The most popular detectors include ionization chambers, proportional counters, Geiger-Mueller counters, scintillation detectors, semiconductor diode detectors (also referred herein as electronic sensor or electronic detector), and dosimeters such as Thermoluminescence Dosimeters (TLD), Optically Simulated Luminescence (OSL), RadioLuminescence Glass (RLG), X-ray film, and track etch. Track-etch type dosimeters are usually used for monitoring high Linear Energy Transfer (LET) particles, such as alpha particles and neutrons. Many other radiation dosimeters comprising a material which changes color or which change in other physical and chemical properties are reported in literature. Individually, or collectively, these devices for monitoring radiation are referred to as dosimeter(s).
X-ray film, TLD, RLG, and OSL are widely used for monitoring personal exposure to radiation. They are highly sensitive (e.g., monitor very low dose, e.g., 1 millirad) and can monitor radiation over a very wide dose range, e.g., from 1 millirad to over 10,000 rads. They are also very accurate (e.g., accuracy of about 5%). Companies offering services to monitor radiation using these dosimeters/sensors normally require their facilities, sensors, dosimeters and processes for monitoring radiation validated by a an organization, often a government agency (such as NAVLAP (National Voluntary Laboratory Accreditation) in the USA, a non-profit or an independent organization. X-ray film, TLD, RLG, OSL and alike sensors and dosimeters are referred herein as accredited or validated sensors and/or accredited dosimeters and the methods used as for determination of the dose as accredited or validated methods or processes. However, they are not instant and self-reading. They need to be sent to a laboratory for determination of the dose, which may take several days.
A number of patents have been issued on film, TLD, RLG, and OSL type radiation dosimeters.
Luminescence techniques in radiation dosimetry have traditionally been dominated by thermal methods in which a sample, such as a ThermoLuminescence Dosimeter or TLD, is exposed to radiation and then heated in the dark. At a certain temperature, or within a certain temperature range, luminescence (light) is emitted from the material. The intensity is related, by calibration procedures, to the original absorbed dose of radiation.
However, in many circumstances, optically stimulated luminescence (OSL) has proven to be a superior method of measuring radiation dose. Generally speaking, OSL methods illuminate a previously irradiated dosimeter with light of a particular frequency and intensity. This exposure excites light production within the dosimeter by transfer of charges from traps to luminescence centers. Then, by measuring the intensity and duration of the resulting luminescence signal that is emitted from the dosimeter, an accurate measure of the amount of radiation to which the dosimeter was exposed can be obtained. Methods and dosimeters employing optically stimulated luminescence in the detection of radiation exposures in various configurations are described in U.S. Pat. Nos. 5,030,834; 5,091,653; 5,567,948; 5,569,927; 5,732,590; 5,811,822; 5,892,234; 5,962,857; 6,087,666, 6,316,782; and 6,414,324.
Previously, glass has been considered as potential TLD and OSL phosphors since it was recognized that the optical transparency of it offers the advantage of more efficient light collection. For example, U.S. Pat. No. 5,656,815 to Huston et al. reports the use of glass as a dosimeter. U.S. Pat. No. 5,811,822 to Huston et al. describes novel glass phosphor materials that exhibit highly favorable characteristics for OSL dosimetry applications. Radiophotoluminescent glass (RLG) dosimetry uses a silver activated meta-phosphate glass sheet. Irradiated plates are imaged with a CCD camera as a UV light depopulates the photostimulable phosphor traps emitting visible light. Other dosimeters include: alanine/Electron Proton Resonance (EPR) dosimetry, Nuclear Magnetic Resonance (NMR) technique for measurement of dose in case of ferrous iron dosimeter and a change in conductivity.
Color changing/developing Self-indicating Instant Radiation Alert Dosimeters (SIRAD) for monitoring low dose, e.g., 0.1 to 1,000 rads, have been reported in U.S. Pat. Nos. 5,420,000, 7,727,158 and PCT applications WO2004017095 and PCT/US2004005860 each of which is incorporated by reference. These documents describe detectors which are commercially available from JP Laboratories Inc., Middlesex, N.J. under trademark of SIRAD®.
Materials used in the sensing strip of SIRAD are a unique class of compounds called diacetylenes with a general formula R′—C≡C—C≡C—R″, wherein R′ and R″ are substituent groups. Diacetylenes are colorless solid monomers. They usually form red or blue-colored polymers/plastics with a general formula [═(R′)C—C≡C—C(R″)═]n, when irradiated with high energy radiation, such as X-ray, gamma ray, electrons, and neutrons. As exposure to radiation increases, the color of the sensing strip comprising diacetylenes intensifies proportional to the dose.
U.S. Pat. No. 7,727,158 to Patel at el discloses a SIRAD sensor in the form of a label or sticker which is applied on a detector or dosimeter. A drawback of this device is that it is not tamper resistant; the SIRAD sticker can be peeled off. The conventional or accredited TLD, OSL, RLG, and X-ray film dosimeters are specially designed for occupational radiation workers and hence are expensive and need to be returned, whether a SIRAD sticker/label is applied or not. Credit card sized TLD dosimeters, commonly known as wallet cards or dosimeters, are less expensive which can be used by non-occupation workers. The chips are typically loose in plastic cards, the cards are very thick and not carried by everybody routinely like a credit card. Additionally, the TLD chips are typically not encapsulated and sealed in the wallet cards. An improved composite, one piece, less expensive, tamper resistant, multi sensor dosimeter, at least one of the sensors being a color developing, such as SIRAD to warn the user of exposure to high dose, usually non-occupational workers, of radiation exposure and the other sensor being the conventional sensor, including electronic devices such as semiconductors, TLD, OSL, RLG, or X-ray film is described by Patel in U.S. patent application Ser. No. 12/294,148 entitled “A Self Indicating Multi-sensor Radiation Dosimeter”. These devices are bulky and not suitable for individual use. This type of dosimeter(s) having more than one sensor are described herein as multi-sensor dosimeter(s), multi-sensor device, SIRAD multi-sensor(s), or SIRAD-multi-sensor dosimeter(s). Self-indicating, color changing or color developing dosimeters and sensors are referred herein to as self-indicating radiation sensor, SIRAD sensor(s) or SIRAD dosimeter(s) or simply SIRAD. The TLD, OSL, RLG, X-ray, track-etch, electronic type dosimeters or sensors, including doped glass/ceramic and polymeric are individually or collectively referred to as accurate, precision, readable, accredited or simply as the other, second or conventional dosimeter(s) or sensor(s).
Most of the users, including the radiation occupational workers, of radiation dosimeters receive no more than the background dose or a dose which is negligibly higher than the background dose. However, they do not see or determine their exposure. They return the dosimeter to a service provider for determination of the exposure on some predetermined schedule regardless of possible radiation exposures between test dates. Critical time is lost between the actual exposure and the detection therefore the ability to mitigate the exposure is severely hindered. Furthermore, every badge would need to be read which leads to inherent waste and excessive cost. Hence, there is a need for a disposal dosimeter which can determine when, and if, the user should return the dosimeter earlier for accurate reading by validated or accredited methods.
In the case of a detonation of a dirty bomb by terrorists, a nuclear bomb, or a major accident at a nuclear power plant, first responders, medical personnel, and the general public need to know, “Did I receive an acceptable low or a lethal dose of ionizing radiation?” Hence there is need to know the dose instantly and with high accuracy. In the event of a radiological incident, affected people would panic and be worried throughout their lives about the exposure to radiation. The panic and stampede can cause injuries and deaths. It is very difficult to measure low dose in humans. One can estimate dose by analyzing blood if the dose is higher than about 25 rads. There is also a possibility of lawsuits. In order to minimize the panic and worry, there is a strong need to provide a dosimeter in a form which most of us carry almost all the time. However, this is not practical with the typical conventional dosimeters.
In an event of a radiological incident, the dosimeters preferably are to be read at a very high speed e.g., from a hundred to thousands a minute. Hence, there is also a need for a machine readable dosimeter which can be read at a very high speed. Disclosed herein is an Identification Personal Dosimeter (IDPD) which identifies to an individual, his/her approximate exposure to radiation immediately and which has a sensor which can be accurately read by a machine at a very high speed if warranted.